An audio equalizer (AEQ) is commonly configured to enhance or weaken different frequency components of an audio signal, so as to adjust a tone of the audio signal according to auditory preferences of a user, thereby improving the user's auditory experience. A parametric digital AEQ is equivalent to a high-order IIR digital filter in terms of principle, and its frequency response is determined only based on a transfer function of the high-order digital filter. At a landmark of DSP, a quantization error of a filter factor may make an actual frequency response of an AEQ landmark model to deviate from the design principle. In view of this, the above high-order IIR filter may be divided into a plurality of low-order filters (including a biquad filter and/or a double first-order filter) connected in series, and the overall structure thereof is shown in FIG. 1. In terms of mathematics, the AEQ may be represented as a high-order IIR filter with the following transfer function:
                                          H            AEQ                    ⁡                      (            z            )                          =                                                            ∑                                  k                  =                  0                                M                            ⁢                                                b                  k                                ⁢                                  z                                      -                    k                                                                                      1              +                                                ∑                                      k                    =                    0                                    N                                ⁢                                                      a                    k                                    ⁢                                      z                                          -                      k                                                                                                    ⁢                      :                                                        (          1          )                ,            N≥M, and {bk} and {ak} are filter factors.
The above formula may be decomposited as:HAEQ(Z)=Πk=1RHk(z)  (2)
R is the integer part of (N+1)/2, Hk(Z) is a kth-stage low-order filter. In the case that the filter is implemented based on an all-pass filter structure, the transfer function may be represented as:
                                          H            k                    ⁡                      (            z            )                          =                  {                                                                                                                                        F                                                  k                          ⁢                                                                                                          ⁢                          g                                                                    ·                                                                                                    a                                                          k                              ⁢                                                                                                                          ⁢                              0                                                                                +                                                                                    a                                                              k                                ⁢                                                                                                                                  ⁢                                1                                                                                      ·                                                          z                                                              -                                1                                                                                                              +                                                      z                                                          -                              2                                                                                                                                1                          +                                                                                    a                                                              k                                ⁢                                                                                                                                  ⁢                                1                                                                                      ·                                                          z                                                              -                                1                                                                                                              +                                                                                    a                                                              k                                ⁢                                                                                                                                  ⁢                                0                                                                                      ·                                                          z                                                              -                                2                                                                                                                                                                          +                                          B                      kg                                                        ,                                                                                                  in                    ⁢                                                                                  ⁢                    the                    ⁢                                                                                  ⁢                    case                    ⁢                                                                                  ⁢                    that                    ⁢                                                                                  ⁢                                          a                                              k                        ⁢                                                                                                  ⁢                        0                                                                              ≠                  0                                                                                                                                                                        F                        kg                                            ·                                                                                                    a                                                          k                              ⁢                                                                                                                          ⁢                              1                                                                                +                                                      z                                                          -                              1                                                                                                                                1                          +                                                                                    a                                                              k                                ⁢                                                                                                                                  ⁢                                1                                                                                      ·                                                          z                                                              -                                1                                                                                                                                                                          +                                          B                      kg                                                        ,                                                                                                  in                    ⁢                                                                                  ⁢                    the                    ⁢                                                                                  ⁢                    case                    ⁢                                                                                  ⁢                    that                    ⁢                                                                                  ⁢                                          a                                              k                        ⁢                                                                                                  ⁢                        0                                                                              =                  0                                                                                        (        3        )            
{aki, i−0, 1} is an all-pass filter factor in the kth stage, and {Bkg, Fkg} are respectively a gain of a bypass branch and a gain of a filter branch of the kth-stage filter.
The kth-stage low-order filter defined by the above formula (3) has a structure shown in FIG. 2.
A parameter set {ak0, ak1, Bkg, Fkg, k=1, 2, . . . , R} of all the low-order filters forms a parameter preset of the AEQ which defines a system frequency response curve of the AEQ.
In the related art, when playing the audio signal, a noise sound like “Click” may occur when switching the preset set of the AEQ, which may makes the user uncomfortable.